Projection lens unit of projector and projector

ABSTRACT

A projection lens unit (15) of a projector (10) is disposed in a state in which an optical axis (CL) of the projection lens unit deviates from a center of an image forming panel (14); a first lens holder (43) of a lens barrel (40) includes holding pieces (55a, 55b) that are provided at intervals in a circumferential direction of a first lens group (L1) and are engaged with a first portion (A1) of the first lens group positioned on a side to which the image forming panel is shifted, and a holding piece (55c) that is engaged with a second portion (A2) of the first lens group positioned on a side opposite to the side to which the image forming panel is shifted; and the linear expansion coefficient of each of the holding pieces is lower than the linear expansion coefficient of the holding piece.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of and claims the priority benefit ofa prior application Ser. No. 16/013,945 filed on Jun. 21, 2018, nowallowed. The prior application Ser. No. 16/013,945 is a Continuation ofPCT International Application No. PCT/JP2016/086567 filed on Dec. 8,2016, which claims priority under 35 U.S.C § 119(a) to Japanese PatentApplication No. 2016-016204 filed on Jan. 29, 2016. Each of the aboveapplication(s) is hereby expressly incorporated by reference, in itsentirety, into the present application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a projection lens unit of a projectorand a projector.

2. Description of the Related Art

A projector projects light, which is applied to an image forming panelfrom a light source, onto a projection surface through a projection lensunit to display an image. In a recent projector, the illuminance of aprojected image has been further improved through the improvement of animage forming panel and a light source than in the related art. As aresult, unnecessary light, which does not contribute to the formation ofan image, is also increased, and the temperature of a lens barrel of aprojection lens unit becomes higher than that in the related art in acase in which the unnecessary light is removed by the lens barrel or alight screen of the projection lens unit.

In a projector disclosed in JP2005-128217A, a reflective region isprovided on a portion, which receives unnecessary light, of a lensholder, a stop, or the like of a lens barrel and the absorption ofunnecessary light is suppressed. Accordingly, a rise in the temperatureof the lens barrel is suppressed, so that the deformation of the lensbarrel caused by a rise in temperature is suppressed.

In a projector disclosed in JP2014-59333A, an unnecessarylight-receiving member overlaps with a lens holder of a lens barrel, andthe surface of a contact portion of the lens holder, which is in contactwith the unnecessary light-receiving member, is formed in an unevenshape. Accordingly, the transfer of heat to the lens holder from theunnecessary light-receiving member is reduced in comparison with a casein which the entire surface of the unnecessary light-receiving member isin contact with the lens holder. Therefore, a rise in the temperature ofthe lens barrel is suppressed, so that the deformation of the lensbarrel caused by a rise in temperature is suppressed.

Further, the following projectors are known. The projectors are adaptedto displace a lens group, which is held by a holding member, in thedirection of an optical axis through the thermal expansion of theholding member holding some lenses of a lens barrel against the changeof a focal position, which occurs due to the deformation of the lensbarrel caused by heat, to correct the change of the focal position (forexample, JP2009-271448A and JP2012-242728A).

SUMMARY OF THE INVENTION

In a wide-angle projector that can perform short-distance projection,there is a case where the optical axis of a projection lens unit isdisposed to deviate from the center of an image forming panel so thatthe projector projects light onto a screen, where the screen is locatedat a position higher than the position of a main body of the projectorin a state in which the main body of the projector is installed on atable. In this case, since a deviation occurs in the projection ofunnecessary light onto the lens barrel, distribution is caused in thetemperature of the lens barrel in the circumferential direction. As aresult, distribution in a circumferential direction is caused in thethermal expansion of the lens barrel in the direction of the opticalaxis and the inclination of a lens group with respect to the opticalaxis of the projection lens unit is caused. For this reason, there is aconcern that image quality may deteriorate.

In the projectors disclosed in JP2005-128217A and JP2014-59333A, thetemperature distribution of the lens barrel in the circumferentialdirection is not canceled and the inclination of the lens group causedby the temperature distribution of the lens barrel in thecircumferential direction is not canceled. Even in the projectorsdisclosed in JP2009-271448A and JP2012-242728A, the lens group is merelydisplaced in the direction of the optical axis through the thermalexpansion of the holding member and the inclination of the lens groupcaused by the temperature distribution of the lens barrel in thecircumferential direction is not canceled.

The invention has been made in consideration of the above-mentionedcircumstances, and an object of the invention is to provide a projectionlens unit and a projector that can suppress the deterioration of animage caused by temperature distribution of a lens barrel in acircumferential direction.

A projection lens unit according to an aspect of the invention is aprojection lens unit of a projector projecting light, which is appliedto an image forming panel from a light source, onto a projection surfaceas image light and disposed in a state in which an optical axis of theprojection lens unit deviates from a center of the image forming panel.The projection lens unit comprises a lens barrel that is provided withone or more lens groups and one or more lens holders holding the lensgroups, respectively. At least one of the lens holders includes aplurality of holding pieces that are provided at intervals in acircumferential direction of the lens group held by the lens holder andare engaged with an outer peripheral portion of the lens group, of afirst portion and a second portion of the lens group where the lensgroup is divided as to the two portions by a plane perpendicular to ashift direction in which the image forming panel is shifted from theoptical axis and including the optical axis, the plurality of holdingpieces including one or more holding pieces engaged with the firstportion, which is positioned on a side to which the image forming panelis shifted, and one or more holding pieces engaged with the secondportion that is positioned on a side opposite to the side to which theimage forming panel is shifted. A linear expansion coefficient of afirst material, which forms the holding pieces engaged with the firstportion, is lower than a linear expansion coefficient of a secondmaterial that forms the holding pieces engaged with the second portion.

Further, a projector according to an aspect of the invention comprisesthe projection lens unit, an image forming panel that is disposed suchthat a center of the image forming panel deviates from an optical axisof the projection lens unit, and a light source that applies light tothe image forming panel.

In a case in which the invention is used, it is possible to provide aprojection lens unit and a projector that can suppress the deteriorationof an image caused by a deviation in the temperature of a lens barrel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example of a projector illustratingan embodiment of the invention.

FIG. 2 is a schematic diagram of a light source of the projector of FIG.1.

FIG. 3 is a longitudinal sectional view of a projection lens unit of theprojector of FIG. 1.

FIG. 4 is a schematic diagram illustrating the shift ratio of an imageforming panel to an optical axis of the projection lens unit.

FIG. 5 is a cross-sectional view of the projection lens unit of FIG. 3taken along line V-V.

FIG. 6 is a perspective view of a first lens holder of the projectionlens unit of FIG. 3.

FIG. 7 is a front view of the first lens holder of FIG. 6.

FIG. 8 is a cross-sectional view of the first lens holder of FIG. 7taken along line VIII-VIII.

FIG. 9 is a perspective view showing a modification example of the firstlens holder of FIG. 6.

FIG. 10 is a front view of the first lens holder of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the structure of an example of a projector illustrating anembodiment of the invention.

In the projector 10 shown in FIG. 1, a light source 13, an image formingpanel 14, a projection lens unit 15, and a control unit 17 are receivedin a case 11. A zoom dial 21, a light quantity adjustment dial 22, afocus dial 23, a vertical attitude adjustment dial 24, a horizontalattitude adjustment dial 25, and an image correction dial 26 areprovided on the upper surface of the case 11.

A transmission type liquid crystal panel is used as the image formingpanel 14. The light source 13 is disposed on the back surface of theimage forming panel 14, that is, on the side of the image forming panel14 opposite to the projection lens unit 15. An image is given to light,which is emitted from the light source 13, on an image forming surface14 a of the image forming panel 14, and the light to which the image isgiven is projected onto the projection surface through the projectionlens unit 15 as image light.

The control unit 17 allows a red-green-blue (RGB) color image to bedisplayed on the image forming surface 14 a of the image forming panel14. In addition, the control unit 17 also performs the followingcontrol. For example, in a case in which the control unit 17 receives anoperation signal of the zoom dial 21, the control unit 17 adjusts thesize of the image to be projected onto a screen 20. In a case in whichthe control unit 17 receives an operation signal of the light quantityadjustment dial 22, the control unit 17 adjusts the brightness of theimage to be projected onto the screen 20. In a case in which the controlunit 17 receives an operation signal of the focus dial 23, the controlunit 17 allows a focus adjustment mechanism (not shown) of theprojection lens unit 15 to operate to adjust the focus of a centralportion of the image projected onto the screen 20. In a case in whichthe control unit 17 receives an operation signal of the verticalattitude adjustment dial 24, the control unit 17 allows a first motor ofan attitude adjustment device (not shown) to be driven. Accordingly, thecontrol unit 17 allows the projection lens unit 15 to be rotated about ahorizontal axis orthogonal to an optical axis CL to adjust theinclination of the projection lens unit 15 in an up-down direction. In acase in which the control unit 17 receives an operation signal of thehorizontal attitude adjustment dial 25, the control unit 17 allows asecond motor of the attitude adjustment device to be driven.Accordingly, the control unit 17 allows the projection lens unit 15 tobe rotated about a vertical axis orthogonal to the optical axis CL toadjust the inclination of the projection lens unit 15 in a lateraldirection. In a case in which the control unit 17 receives an operationsignal of the image correction dial 26, the control unit 17 changes thedisplay size and shape of an image to be formed on the image formingsurface 14 a of the image forming panel 14. For example, the controlunit 17 changes the display size and shape of an image so that arectangular image is not displayed as a trapezoidal image according tothe inclination angle of the projection lens unit 15.

FIG. 2 shows the structure of the light source 13.

The light source 13 includes a light emitting diode (LED) 31R that emitsred (R) light, a LED 31G that emits green (G) light, and a LED 31B thatemits blue (B) light. Light emitted from the LED 31R is reflected by adichroic mirror 32. Light emitted from the LED 31G is reflected by adichroic mirror 33, and is transmitted through the dichroic mirror 32.Light emitted from the LED 31B is transmitted through the dichroicmirror 32 and the dichroic mirror 33. Accordingly, three kinds of colorlight, that is, R light, G light, and B light are emitted to the sameoptical path. A xenon lamp, a halogen lamp, or a super high-pressuremercury lamp, which emits white light, may be used instead of the LED31R, the LED 31G, and the LED 31B of the light source 13.

FIG. 3 shows the structure of the projection lens unit 15.

Light emitted from the projection lens unit 15 is projected onto thescreen 20, which is a projection surface, vertically above the opticalaxis CL of the projection lens unit 15, as image light. The center ofthe image forming panel 14 is disposed so as to be shifted from theoptical axis CL in a direction opposite to a direction where the centralposition of the image projected onto the screen 20 is shifted from theoptical axis CL, that is, to the vertically lower side of the opticalaxis CL.

Here, the shift ratio of the image forming panel 14 will be describedwith reference to FIG. 4.

In a case in which a shift amount (distance) between the optical axis CLof the projection lens unit 15 and the center of the image forming panel14 is denoted by Y and the length of the image forming panel 14 in ashift direction is denoted by H, the shift ratio S of the image formingpanel 14 is defined by “S=Y/H”. That is, in the case of “S=0.5”, theupper end face of the image forming panel 14 coincides with the opticalaxis CL of the projection lens unit 15 as shown in FIG. 4. Further, inthe case of “S>0.5 (S is larger than 0.5)”, the image forming panel 14deviates from the optical axis CL of the projection lens unit 15.Furthermore, in the case of “S=0”, the center of the image forming panel14 and the optical axis CL of the projection lens unit 15 coincide witheach other and the disposition of the image forming panel 14 and theprojection lens unit 15 is close to a long-distance projection type inthe related art.

It is preferable that the shift ratio S of the image forming panel 14 isset to exceed 0.4 and to be lower than 0.7. In a case in which the shiftratio S exceeds 0.4, the influence of temperature on the projection lensunit 15 in a vertical direction does not appear in comparison with acase in which the shift ratio S is 0.4 or less. On the other hand, in acase in which the shift ratio S is lower than 0.7, the shift amount Y ofthe image forming panel 14 is not excessively increased, an increase inthe size of a lens system is suppressed, and the deterioration ofmanufacturing suitability is prevented in comparison with a case inwhich the shift ratio S is 0.7 or more. Accordingly, in a case in whichthe shift ratio S of the image forming panel 14 is set in theabove-mentioned range, it is possible to provide a high-performanceproduct while reducing the influence of temperature on the projectionlens unit 15 in the vertical direction. It is more preferable that theshift ratio S of the image forming panel 14 is set to exceed 0.45 and tobe lower than 0.6.

Referring to FIG. 3 again, the projection lens unit 15 includes: sixlens groups, that is, a first lens group L1, a second lens group L2, athird lens group L3, a fourth lens group L4, a fifth lens group L5, anda sixth lens group L6 arranged in this order from the image formingpanel 14; an aperture stop 49 that adjusts the brightness (F-Number) ofthe projection lens unit 15; and a lens barrel 40 that receives thefirst to sixth lens groups L1 to L6 and the aperture stop 49. Each ofthe first to sixth lens groups L1 to L6 is formed of one or a pluralityof lenses.

The structure of each of the first to sixth lens groups L1 to L6 isexemplary, and can be appropriately modified according to an opticaldesign. Further, the aperture stop 49 is disposed between the secondlens group L2 and third lens group L3 in an example shown in FIG. 3, butthe disposition of the aperture stop 49 is also exemplary, and can beappropriately modified according to an optical design.

The lens barrel 40 includes a cylindrical lens barrel body 41, a cambarrel 42, a first lens holder 43, a second lens holder 44, a third lensholder 45, a fourth lens holder 46, a fifth lens holder 47, and a sixthlens holder 48.

The first to sixth lens holders 43 to 48 are disposed in the lens barrelbody 41, the first lens holder 43 holds the first lens group L1, thesecond lens holder 44 holds the second lens group L2, the third lensholder 45 holds the third lens group L3, the fourth lens holder 46 holdsthe fourth lens group L4, the fifth lens holder 47 holds the fifth lensgroup L5, and the sixth lens holder 48 holds the sixth lens group L6.

Further, the first lens holder 43 is fixed to an end portion of the lensbarrel body 41 facing the image forming panel 14, and the sixth lensholder 48 is fixed to an end portion of the lens barrel body 41 facingthe screen 20. Furthermore, the second to fifth lens holders 44 to 47are adapted to be movable in the direction of the optical axis in thelens barrel body 41, and are moved in the direction of the optical axisby the cam barrel 42.

FIG. 5 shows the structure of a mechanism for moving the second lensholder 44.

A plurality of cam pins 52 are mounted on the outer periphery of thesecond lens holder 44 by mounting screws 53. The cam pins 52 protrudeoutward from notches 41 a that are formed at the lens barrel body 41 inparallel with the optical axis CL, and are engaged with cam grooves 42 athat are formed at the cam barrel 42 so as to be inclined with respectto the optical axis CL. In a case in which the cam barrel 42 is rotatedrelative to the lens barrel body 41, the second lens holder 44 is movedin the direction of the optical axis.

Since the third to fifth lens holders 45 to 47 also have the samestructure as the second lens holder 44, the third to fifth lens holders45 to 47 are moved in the direction of the optical axis with therotation of the cam barrel 42. For example, an operation for adjusting afocus, an operation for changing magnification, or the like is performedin a case in which the second to fifth lens holders 44 to 47 areappropriately moved in the direction of the optical axis.

The lens barrel body 41, the cam barrel 42, and the first to sixth lensholders 43 to 48 are made of, for example, a synthetic resin, such aspolycarbonate.

FIGS. 6 to 8 show the structure of the first lens holder 43.

The first lens holder 43 includes a holding piece 55 a, a holding piece55 b, and a holding piece 55 c that are engaged with the outerperipheral portion of the first lens group L1, and a substantiallycylindrical frame portion 56 that supports these three holding pieces.

A plurality of fixing portions 57, which are to be fixed to the lensbarrel body 41, are provided on the outer peripheral surface of theframe portion 56. The fixing portions 57 are provided on the samecircumference on the outer peripheral surface of the frame portion 56,are arranged at substantially regular intervals in a circumferentialdirection, and are formed integrally with the frame portion 56 so as toprotrude outward from the frame portion 56.

The holding piece 55 a, the holding piece 55 b, and the holding piece 55c are provided on an inner edge portion of one end face of the frameportion 56 at substantially regular intervals in the circumferentialdirection, and are formed integrally with the frame portion 56 so as toprotrude from the frame portion 56 along the optical axis CL of theprojection lens unit 15. The distal end portion of each of the holdingpiece 55 a, the holding piece 55 b, and the holding piece 55 c areengaged with the outer peripheral portion of the first lens group L1 atsubstantially regular intervals in the circumferential direction of thefirst lens group L1.

In a case in which the first lens group L1 is divided into a firstportion A1 positioned on a side to which the image forming panel 14 isshifted (vertically lower side) and a second portion A2 positioned on aside opposite to the side to which the image forming panel 14 is shifted(vertically upper side) by a plane B that is perpendicular to the shiftdirection where the image forming panel 14 is shifted from the opticalaxis CL of the projection lens unit 15 and includes the optical axis CL,as shown in FIG. 7, the holding pieces 55 a and 55 b are engaged withthe first portion A1 and the holding piece 55 c is engaged with thesecond portion A2. Further, the linear expansion coefficient of each ofthe holding pieces 55 a and 55 b to be engaged with the first portion A1is set to be lower than the linear expansion coefficient of the holdingpiece 55 c to be engaged with the second portion A2.

The above-mentioned first lens holder 43 can be produced, for example,as described below by multi-color molding using different resinmaterials. First, the holding piece 55 c and the frame portion 56 areprimarily molded integrally with each other using a second resinmaterial. Next, only a cavity mold of a core mold and a cavity mold usedin the primary molding is exchanged, and the holding pieces 55 a and 55b are secondarily molded integrally with the primarily molded body,which is formed of the holding piece 55 c and the frame portion 56,using a first resin material of which the linear expansion coefficientis lower than the linear expansion coefficient of the second resinmaterial. Accordingly, the first lens holder 43, of which the holdingpieces 55 a, 55 b, and 55 c are integrated with the frame portion 56 andthe linear expansion coefficient of each of the holding pieces 55 a and55 b to be engaged with the first portion A1 is lower than the linearexpansion coefficient of the holding piece 55 c to be engaged with thesecond portion A2, is obtained.

Further, the first lens holder 43 can also be produced, for example, asdescribed below by insert molding. First, the holding pieces 55 a and 55b are produced in advance using the first resin material. Next, theholding pieces 55 a and 55 b, which have been produced in advance, areinserted into a mold for integrally molding the holding piece 55 c andthe frame portion 56, and the mold is filled with the second resinmaterial to mold the holding piece 55 c and the frame portion 56integrally with the holding pieces 55 a and 55 b in a state in which theholding pieces 55 a and 55 b are inserted into the mold. Accordingly,the first lens holder 43, of which the holding pieces 55 a, 55 b, and 55c are integrated with the frame portion 56 and the linear expansioncoefficient of each of the holding pieces 55 a and 55 b to be engagedwith the first portion A1 is lower than the linear expansion coefficientof the holding piece 55 c to be engaged with the second portion A2, isobtained.

In terms of increasing the joint strength between the holding pieces 55a and 55 b made of the first resin material and the frame portion 56made of the second resin material, it is preferable that compatibilitybetween the first and second resin materials is high in all of themulti-color molding and the insert molding. Accordingly, it ispreferable that composite materials, which are obtained by addingfillers to a common resin base material and have different linearexpansion coefficients according to the filler contents, are used as thefirst and second resin materials. The filler is an additive to be addedto the resin base material. Particularly, in this specification, thefiller means a material that adjusts the linear expansion coefficient ofthe resin base material according to the amount thereof to be added. Forexample, in a case in which polycarbonate is used as the resin basematerial and a glass fiber is used as the filler, the linear expansioncoefficient of a simple substance of polycarbonate is 6.5×10⁻⁵/° C., thelinear expansion coefficient of a composite material of which thecontent percentage of a glass fiber per unit weight is 20% is 2.5×10⁻⁵/°C., and the linear expansion coefficient of a composite material ofwhich the content percentage of a glass fiber per unit weight is 40% is1.9×10⁻⁵/° C.

Further, at least one of the holding pieces 55 a and 55 b or the holdingpiece 55 c may be formed separately from the frame portion 56, and theseparately formed holding piece may adhere to the frame portion 56 ormay be fitted to the frame portion 56 so as to be joined to the frameportion 56. In this case, it is easy to manage the dimensions of eachmember. Furthermore, the structure of a mold can also be simplified incomparison with a case in which the holding pieces 55 a and 55 b, theholding piece 55 c, and the frame portion 56 are integrally molded.Moreover, since stable joint strength can be obtained between the frameportion 56 and the holding piece formed separately from the frameportion 56 regardless of compatibility between the material of the frameportion 56 and the material of the holding piece formed separately fromthe frame portion 56, the holding piece formed separately from the frameportion 56 can be made of various materials, such as metal, instead of aresin.

Next, the meaning of making the linear expansion coefficient of each ofthe holding pieces 55 a and 55 b be lower than the linear expansioncoefficient of the holding piece 55 c will be described with referenceto FIG. 8.

Light, which is more than the light applied to the holding piece 55 cengaged with the second portion A2 of the first lens group L1 positionedon the side opposite to the side to which the image forming panel 14 isshifted, is applied to the holding pieces 55 a and 55 b, which areengaged with the first portion A1 of the first lens group L1 positionedon the side to which the image forming panel 14 is shifted, from thelight source 13. As a result, the temperature of each of the holdingpieces 55 a and 55 b becomes higher than the temperature of the holdingpiece 55 c due to the turning-on of the light source 13.

A rise in the temperature of each of the holding pieces 55 a and 55 band the holding piece 55 c, which is caused by the turning-on of thelight source 13, is also changed depending on the quantity of light,which is emitted from the light source 13, per unit time, or the like.However, here, it is assumed that the temperature of each of the holdingpieces 55 a and 55 b rises up to 80° C. from the room temperature (25°C.) and the temperature of the holding piece 55 c rises up to 40° C.from the room temperature.

Further, the diameter of the first lens group L1 is set to 20 mm; adistance a between each fixing portion 57 of the frame portion 56, whichis fixed to the lens barrel body 41, and the proximal end portion ofeach of the holding pieces 55 a and 55 b and the holding piece 55 c inthe direction of the optical axis is set to 5 mm; and a distance bbetween the proximal end portion of each of the holding pieces 55 a and55 b and the holding piece 55 c and a distal end portion of each holdingpiece, which is a portion of each holding piece engaged with the outerperipheral portion of the first lens group L1, in the direction of theoptical axis is set to 30 mm.

First, in a case in which all of the holding pieces 55 a and 55 b, theholding piece 55 c, and the frame portion 56 are made of a simplesubstance of polycarbonate (linear expansion coefficient: 6.5×10⁻⁵/° C.)and the temperature of each of the holding pieces 55 a and 55 b rises upto 80° C. from the room temperature (25° C.) due to the turning-on ofthe light source 13, a change in a distance a+b between the fixingportion 57 and the distal end portion of each of the holding pieces 55 aand 55 b becomes “(80° C.−25° C.)×6.5×10⁻⁵/° C.35 mm≅12.5×10⁻² mm”. Onthe other hand, in a case in which the temperature of the holding piece55 c rises up to 40° C. from the room temperature due to the turning-onof the light source 13, a change in the distance a+b between the fixingportion 57 and the distal end portion of the holding piece 55 c becomes“(40° C.−25° C.)×6.5×10 ⁻⁵/° C.×35≅4.6×10⁻² mm”. In this case, theinclination of the first lens group L1 with respect to a planeperpendicular to the optical axis CL corresponds to 0.2°.

Next, in a case in which each of the holding pieces 55 a and 55 b ismade of a composite material (linear expansion coefficient: 1.9×10⁻⁵/°C.) in which 40% of a glass fiber per unit weight is contained inpolycarbonate, each of the holding piece 55 c and the frame portion 56is made of a simple substance of polycarbonate (linear expansioncoefficient 6.5×10⁻⁵/° C.), and the temperature of each of the holdingpieces 55 a and 55 b rises up to 80° C. from the room temperature (25°C.) due to the turning-on of the light source 13, a change in thedistance a+b between the fixing portion 57 and the distal end portion ofeach of the holding pieces 55 a and 55 b becomes “(80° C.−25°C.)×6.5×10⁻⁵/° C.×5 mm+(80° C.-25° C.)×1.9×10⁻⁵/° C.×30 mm≅4.9×10⁻² mm”.On the other hand, in a case in which the temperature of the holdingpiece 55 c rises up to 40° C. from the room temperature due to theturning-on of the light source 13, a change in the distance a+b betweenthe fixing portion 57 and the distal end portion of the holding piece 55c becomes “(40° C.−25° C.)×6.5×10⁻⁵/° C.×35 mm≅4.6×10⁻² mm”. In thiscase, the inclination of the first lens group L1 with respect to a planeperpendicular to the optical axis CL corresponds to 0.0008°.

In a case in which the linear expansion coefficient of each of theholding pieces 55 a and 55 b to be engaged with the first portion A1 ofthe first lens group L1, which is positioned on the side to which theimage forming panel 14 is shifted, is set to be lower than the linearexpansion coefficient of the holding piece 55 c to be engaged with thesecond portion A2 of the first lens group L1 that is positioned on theside opposite to the side to which the image forming panel 14 is shiftedas described above, it is possible to suppress the inclination of thefirst lens group L1 that is caused by the temperature distribution ofthe lens barrel 40 in the circumferential direction. Accordingly, it ispossible to suppress the deterioration of an image.

The first lens holder 43 provided with three holding pieces, that is,the holding pieces 55 a, 55 b, and 55 c has been described so far, butthe first lens holder 43 may include one or more holding pieces to beengaged with the first portion A1 of the first lens group L1 and one ormore holding pieces to be engaged with the second portion A2 of thefirst lens group L1.

FIGS. 9 and 10 show the structure of a modification example of the firstlens holder 43, and the first lens holder 43 includes one holding piece55 d to be engaged with the first portion A1 of the first lens group L1and one holding piece 55 e to be engaged with the second portion A2 ofthe first lens group L1. The linear expansion coefficient of the holdingpiece 55 d to be engaged with the first portion A1 is set to be lowerthan the linear expansion coefficient of the holding piece 55 e to beengaged with the second portion A2.

The holding pieces 55 d and 55 e have a structure in which asubstantially cylindrical frame body coaxial with the optical axis CL ofthe projection lens unit 15 is formed on an inner edge portion of oneend face of the frame portion 56. Further, the holding pieces 55 d and55 e have a structure in which two slits 58 extending parallel to theoptical axis CL are formed at portions of the frame body crossing aplane B dividing the first lens group L1 into a first portion A1 and asecond portion A2 and the frame body is divided from each other in thecircumferential direction by the slits 58.

In a case in which the linear expansion coefficient of the holding piece55 d to be engaged with the first portion A1 of the first lens group L1,which is positioned on the side to which the image forming panel 14 isshifted, is set to be lower than the linear expansion coefficient of theholding piece 55 e to be engaged with the second portion A2 of the firstlens group L1 that is positioned on the side opposite to the side towhich the image forming panel 14 is shifted, it is possible to suppressthe inclination of the first lens group L1, which is caused by thetemperature distribution of the lens barrel 40 in the circumferentialdirection, even in the first lens holder 43 of this modificationexample. Accordingly, it is possible to suppress the deterioration of animage.

Further, it is possible to produce the first lens holder 43 of thismodification example by multi-color molding using different resinmaterials or insert molding as in the case of the first lens holder 43shown in FIGS. 6 to 8, or it is also possible to produce the first lensholder 43 by forming at least one of the holding piece 55 d or theholding piece 55 e separately from the frame portion 56 and joining theseparately formed holding piece to the frame portion 56. Since theholding pieces 55 d and 55 e are larger than the holding pieces 55 a and55 b and the holding piece 55 c of the first lens holder 43 shown inFIGS. 6 to 8, it is easy to produce the first lens holder 43 even thoughthe first lens holder 43 is produced by any method of them.

A structure in which the linear expansion coefficient of the holdingpiece to be engaged with the first portion A1 of the first lens group L1positioned on the side, to which the image forming panel 14 is shifted,among the plurality of holding pieces of the first lens holder 43 is setto be lower than the linear expansion coefficient of the holding pieceto be engaged with the second portion A2 of the first lens group L1positioned on the side opposite to the side, to which the image formingpanel 14 is shifted, has been described above by using the first lensholder 43, which is fixed to the end portion of the lens barrel body 41facing the image forming panel 14, among the first to sixth lens holders43 to 48, as an example. However, the above-mentioned structure of thefirst lens holder 43 can also be used for the other lens holders.Particularly, since the deviation of light applied from the light source13 is relatively large in the second lens holder 44 disposed closer tothe image forming panel 14 than the aperture stop 49 as in the firstlens holder 43, the above-mentioned structure of the first lens holder43 can also be suitably used for the second lens holder 44.

Further, the transmission type liquid crystal panel is used as the imageforming panel 14 in the embodiment, but a reflection type liquid crystalpanel or a digital micro mirror device (DMD) can also be used. In thiscase, the light of the light source 13 is applied to the front surfaceof the image forming panel from the front side of the image formingpanel 14 through an illumination optical system using a known prism (notshown) and the like.

As described above, a projection lens unit disclosed in thisspecification projects light, which is applied to an image forming panelfrom a light source, onto a projection surface as image light and isdisposed in a state in which an optical axis of the projection lens unitdeviates from a center of the image forming panel. The projection lensunit of a projector includes a lens barrel that is provided with one ormore lens groups and one or more lens holders holding the lens groups,respectively. At least one of the lens holders includes a plurality ofholding pieces that are provided at intervals in a circumferentialdirection of the lens group held by the lens holder and are engaged withan outer peripheral portion of the lens group. Of a first portion and asecond portion of the lens group where the lens group is divided as tothe two portions by a plane perpendicular to a shift direction in whichthe image forming panel is shifted from the optical axis and includingthe optical axis, the plurality of holding pieces include one or moreholding pieces engaged with the first portion, which is positioned on aside to which the image forming panel is shifted, and one or moreholding pieces engaged with the second portion that is positioned on aside opposite to the side to which the image forming panel is shifted. Alinear expansion coefficient of a first material, which forms theholding pieces engaged with the first portion, is lower than a linearexpansion coefficient of a second material that forms the holding piecesengaged with the second portion.

Further, in the projection lens unit disclosed in this specification,the lens holder including the holding pieces further includes a frameportion that supports the holding pieces, the frame portion and theholding pieces are made of a resin material and are integrated with eachother, and a first resin material as the first material, which forms theholding pieces engaged with the first portion, and a resin material,which forms the holding pieces engaged with the second portion, areformed of second resin materials as second materials having differentlinear expansion coefficients, respectively.

Furthermore, in the projection lens unit disclosed in thisspecification, the lens holder including the holding pieces furtherincludes a frame portion that supports the holding pieces, and at leastone of the holding pieces engaged with the first portion and the holdingpieces engaged with the second portion is formed separately from theframe portion and is joined to the frame portion.

Moreover, in the projection lens unit disclosed in this specification,the first material which forms the holding pieces engaged with the firstportion and the second material which forms the holding pieces engagedwith the second portion are composite materials, which are obtained byadding fillers for adjusting linear expansion coefficients to a commonresin base material, and content percentages of the fillers aredifferent from each other.

The projection lens unit disclosed in this specification furtherincludes an aperture stop, and the lens holder, which holds the lensgroup disposed closer to the image forming panel than the aperture stop,includes the holding pieces.

A projector disclosed in this specification includes an image formingpanel that is disposed such that a center of the image forming paneldeviates from an optical axis of the projection lens unit, and a lightsource that applies light to the image forming panel.

Further, in the projector disclosed in this specification, in a case inwhich a distance between the optical axis of the projection lens unitand a center of the image forming panel is denoted by Y, a length of theimage forming panel in a shift direction where the image forming panelis shifted from the optical axis is denoted by H, and a shift ratio ofthe image forming panel obtained by dividing the length H into thedistance Y is defined by “S=Y/H”, and “0.4<S<0.7” is satisfied.

EXPLANATION OF REFERENCES

10: projector

11: case

13: light source

14: image forming panel

14 a: image forming surface

15: projection lens unit

17: control unit

20: screen (projection surface)

21: zoom dial

22: light amount adjustment dial

23: focus dial

24: vertical attitude adjustment dial

25: horizontal attitude adjustment dial

26: image correction dial

32: dichroic mirror

33: dichroic mirror

40: lens barrel

41: lens barrel body

42: cam barrel

42 a: cam groove

43: first lens holder

44: second lens holder

45: third lens holder

46: fourth lens holder

47: fifth lens holder

48: sixth lens holder

49: aperture stop

52: cam pin

53: mounting screw

55 a: holding piece

55 b: holding piece

55 c: holding piece

55 d: holding piece

55 e: holding piece

56: frame portion

57: fixing portion

A1: first portion

A2: second portion

B: plane

CL: optical axis

L1: first lens group

L2: second lens group

L3: third lens group

L4: fourth lens group

L5: fifth lens group

L6: sixth lens group

What is claimed is:
 1. A projection lens unit of a projector, which isdisposed in a state in which an optical axis of the projection lens unitdeviates from a center of an image forming panel of the projector, theprojection lens unit comprising: a lens barrel that is provided with oneor more lens groups and a lens holder holding one or more the lensgroups, wherein the lens holder includes a first part that is formed ofa first material and a second part that is formed of a second material,wherein the first part is on a side of the lens holder where the imageforming panel is shifted with respect to the optical axis of theprojection lens unit, wherein the first part is positioned closer to theimage forming panel than the second part, and wherein a linear expansioncoefficient of the first material is lower than a linear expansioncoefficient of the second material.
 2. The projection lens unitaccording to claim 1, wherein the lens holder holds a lens group of thelens groups disposed on a side closest to the image forming panel in thelens barrel.
 3. The projection lens unit according to claim 1, whereinthe first part is engaged with the second part and extends in aperipheral direction of the lens group.
 4. The projection lens unitaccording to claim 2, wherein the first part is engaged with the secondpart and extends in a peripheral direction of the lens group.
 5. Theprojection lens unit according to claim 1, wherein the second part is aframe portion.
 6. The projection lens unit according to claim 2, whereinthe second part is a frame portion.
 7. The projection lens unitaccording to claim 3, wherein the second part is a frame portion.
 8. Theprojection lens unit according to claim 4, wherein the second part is aframe portion.
 9. The projection lens unit according to claim 1, whereinthe second part has a plane surface and the first part is disposedcloser to the image forming panel than the plane surface of the secondpart.
 10. The projection lens unit according to claim 2, wherein thesecond part has a plane surface and the first part is disposed closer tothe image forming panel than the plane surface of the second part. 11.The projection lens unit according to claim 3, wherein the second parthas a plane surface and the first part is disposed closer to the imageforming panel than the plane surface of the second part.
 12. Theprojection lens unit according to claim 4, wherein the second part has aplane surface and the first part is disposed closer to the image formingpanel than the plane surface of the second part.
 13. The projection lensunit according to claim 5, wherein the second part has a plane surfaceand the first part is disposed closer to the image forming panel thanthe plane surface of the second part.
 14. The projection lens unitaccording to claim 6, wherein the second part has a plane surface andthe first part is disposed closer to the image forming panel than theplane surface of the second part.
 15. The projection lens unit accordingto claim 7, wherein the second part has a plane surface and the firstpart is disposed closer to the image forming panel than the planesurface of the second part.
 16. The projection lens unit according toclaim 1, wherein the first material is a metal material and the secondmaterial is a resin material.
 17. The projection lens unit according toclaim 1, further comprising: an aperture stop, wherein the lens holderholds the lens group disposed closer to the image forming panel than theaperture stop.
 18. The projection lens unit according to claim 1,wherein the first part is positioned corresponding to the second partthat is positioned on a side opposite to the side to which the imageforming panel is shifted.
 19. A projector comprising: the projectionlens unit according to claim 1; the image forming panel; and a lightsource that applies light to the image forming panel.
 20. The projectoraccording to claim 19, wherein in a case in which a distance between theoptical axis of the projection lens unit and the center of the imageforming panel is denoted by Y, a length of the image forming panel in ashift direction which the image forming panel is shifted from theoptical axis is denoted by H, and a shift ratio of the image formingpanel obtained by dividing the length H into the distance Y is definedby “S=Y/H”, and “0.4<S<0.7” is satisfied.